NetEm \- Network Emulator
.SH SYNOPSIS
.B "tc qdisc ... dev"
-.IR dev " ] "
+.IR DEVICE " ] "
.BR "add netem"
.I OPTIONS
.IR OPTIONS " := [ " LIMIT " ] [ " DELAY " ] [ " LOSS \
-" ] [ " CORRUPT " ] [ " DUPLICATION " ] [ " REORDERING " ]"
+" ] [ " CORRUPT " ] [ " DUPLICATION " ] [ " REORDERING " ][ " RATE " ]"
.IR LIMIT " := "
.B limit
.B duplicate
.IR PERCENT " [ " CORRELATION " ]]"
-.IR REODERING " := "
+.IR REORDERING " := "
.B reorder
.IR PERCENT " [ " CORRELATION " ] [ "
.B gap
.IR DISTANCE " ]"
+.IR RATE " := "
+.B rate
+.IR RATE " [ " PACKETOVERHEAD " [ " CELLSIZE " [ " CELLOVERHEAD " ]]]]"
+
+
.SH DESCRIPTION
NetEm is an enhancement of the Linux traffic control facilities
that allow to add delay, packet loss, duplication and more other
characteristics to packets outgoing from a selected network
-interface. NetEm is build using the existing Quality Of Service (QOS)
+interface. NetEm is built using the existing Quality Of Service (QOS)
and Differentiated Services (diffserv) facilities in the Linux
kernel.
Delay and jitter values are expressed in ms while correlation is percentage.
.SS distribution
-allow the choose the delay distribution. If not specified, the default
-distribution is normal. Additional parameters allow to consider situations in
+allow the user to choose the delay distribution. If not specified, the default
+distribution is Normal. Additional parameters allow to consider situations in
which network has variable delays depending on traffic flows concurring on the
-same path, that causes severeal delay peaks and a tail.
+same path, that causes several delay peaks and a tail.
.SS loss random
adds an independent loss probability to the packets outgoing from the chosen
-network interface. It is also possibile to add a correlation, but this option
-is now deprecated due to the noticed bad behaviour.
+network interface. It is also possible to add a correlation, but this option
+is now deprecated due to the noticed bad behavior.
.SS loss state
adds packet losses according to the 4-state Markov using the transition
-probabilities as input parameters. The parameters p13 is mandatory and if used
+probabilities as input parameters. The parameter p13 is mandatory and if used
alone corresponds to the Bernoulli model. The optional parameters allows to
extend the model to 2-state (p31), 3-state (p23 and p32) and 4-state (p14).
State 1 corresponds to good reception, State 4 to independent losses, State 3
.SS loss gemodel
adds packet losses according to the Gilbert-Elliot loss model or its special
cases (Gilbert, Simple Gilbert and Bernoulli). To use the Bernoulli model, the
-only needed parameter is p while the the others will be set to the default
+only needed parameter is p while the others will be set to the default
values r=1-p, 1-h=1 and 1-k=0. The parameters needed for the Simple Gilbert
model are two (p and r), while three parameters (p, r, 1-h) are needed for the
Gilbert model and four (p, r, 1-h and 1-k) are needed for the Gilbert-Elliot
loss probability in the good state.
.SS corrupt
-allows the emulate the random noise introducing an error in a random position
+allows the emulation of random noise introducing an error in a random position
for a chosen percent of packets. It is also possible to add a correlation
through the proper parameter.
.SS duplicate
-using this option the chosen percent of packets is duplicated before queueing
+using this option the chosen percent of packets is duplicated before queuing
them. It is also possible to add a correlation through the proper parameter.
.SS reorder
-there are two ways to use this option:
+to use reordering, a delay option must be specified. There are two ways to use
+this option (assuming 'delay 10ms' in the options list).
-.B "reorder gap"
-.I 5 10
+.B "reorder "
+.I 25% 50%
+.B "gap"
+.I 5
.br
-in this first example every 5th (10th, 15th) packet is sent immediately while
-other packets are delayed by 10 ms
+in this first example, the first 4 (gap - 1) packets are delayed by 10ms and
+subsequent packets are sent immediately with a probability of 0.25 (with
+correlation of 50% ) or delayed with a probability of 0.75. After a packet is
+reordered, the process restarts i.e. the next 4 packets are delayed and
+subsequent packets are sent immediately or delayed based on reordering
+probability. To cause a repeatable pattern where every 5th packet is reordered
+reliably, a reorder probability of 100% can be used.
.B reorder
.I 25% 50%
.br
in this second example 25% of packets are sent immediately (with correlation of
-50%) while the other are delayed by 10 ms.
+50%) while the others are delayed by 10 ms.
+
+.SS rate
+delay packets based on packet size and is a replacement for
+.IR TBF .
+Rate can be
+specified in common units (e.g. 100kbit). Optional
+.I PACKETOVERHEAD
+(in bytes) specify an per packet overhead and can be negative. A positive value can be
+used to simulate additional link layer headers. A negative value can be used to
+artificial strip the Ethernet header (e.g. -14) and/or simulate a link layer
+header compression scheme. The third parameter - an unsigned value - specify
+the cellsize. Cellsize can be used to simulate link layer schemes. ATM for
+example has an payload cellsize of 48 bytes and 5 byte per cell header. If a
+packet is 50 byte then ATM must use two cells: 2 * 48 bytes payload including 2
+* 5 byte header, thus consume 106 byte on the wire. The last optional value
+.I CELLOVERHEAD
+can be used to specify per cell overhead - for our ATM example 5.
+.I CELLOVERHEAD
+can be negative, but use negative values with caution.
+
+Note that rate throttling is limited by several factors: the kernel clock
+granularity avoid a perfect shaping at a specific level. This will show up in
+an artificial packet compression (bursts). Another influence factor are network
+adapter buffers which can also add artificial delay.
.SH LIMITATIONS
The main known limitation of Netem are related to timer granularity, since
Linux is not a real-time operating system.
+.SH EXAMPLES
+.PP
+tc qdisc add dev eth0 root netem rate 5kbit 20 100 5
+.RS 4
+delay all outgoing packets on device eth0 with a rate of 5kbit, a per packet
+overhead of 20 byte, a cellsize of 100 byte and a per celloverhead of 5 byte:
+.RE
+
.SH SOURCES
.IP " 1. " 4
Hemminger S. , "Network Emulation with NetEm", Open Source Development Lab,
projects / lisovros / iproute2_canprio.git / blobdiff